I'm don't know alot about the amount of timing that is required for certain load points to bring these turbo's on but it's going to be a reasonable difference from the factory stock turbo, same with the fuel adjustment. It's not possibly to adjust that without purchasing a APFC with the SAFC so unfortunately he will have to upgrade or performance might suffer. In terms of the financials you can sell the SAFC are a reasonable used price ($200+?) spend the extra on the APC, around $2000 now for the RB25DET. Alternatively you use the VIPEC or HALTECH which offer good value products. When it comes to tuning it APFC or other units often are around $500 now, SAFC are around $100 or $200 so it is a small difference in considerion for the cash spend on this upgrade. The term shaft is rather harsh, most of the workshop's in Perth are great and you pay for a premium service that your general mechanic cannot do, also been a business they have overheads so paying alittle extra for parts is often acceptable.